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Advancing Kidney Transplants through Data, Donor Chains and Vouchers, Part 1
Over the past decade, kidney transplant specialists have expanded their primary focus from the narrowly circumscribed deceased donor pool to include a virtually unlimited living donor pool. Living kidney donations can reduce the 10-year transplant failure rate by 40 percent.
The potential to expand the living donor pool has been driven by several technological and clinical developments, including:
- Population data software now facilitates matching multiple, specific characteristics, allowing ideal and near-ideal matches on a much larger scale. The National Kidney Registry, the largest repository for donor and recipient information in the world, developed a sophisticated program, BestMatch, to expand the quality and breadth of matches. Today 80 transplant centers participate in the registry.
- Laparoscopic procedures replaced open procedures, which lowered risks, pain and recovery time for donors and recipients.
- New clinical means of combatting incompatibility issues (e.g., highly sensitized patients or those with elevated levels of donor-specific antibody) now exist to prepare patients who would not otherwise be eligible recipients.
In addition, programs have been created to increase the number of living donor options. Most recently, UCLA launched a kidney voucher program, which, by leveraging data software, allows a donor to donate today and secure a voucher for a loved one who may need a kidney later in life.
Historical timeline: from paired swaps to chains
The first four-person donor exchange (or kidney swap or loop) in the U.S. was performed at Rhode Island Hospital in 2000. This approach further released transplantation from the tethers of intrafamily donation. No longer were deceased donors the sole source of a transplant organ when no immediate living donor was available. Yet four-person pairing took a while to catch fire, and was still inadequate to meet the need.
Johns Hopkins later employed the concept of a donor (or domino) chain, orchestrating the first 16-patient, multi-hospital transplant swap in 2009. With a chain, people were able to pay it forward, donating to an unknown recipient, thereby allowing more people to benefit from the gift of the original donor.
A donor chain works in this way. First, a non-directed donor (NDD) (a donor who does not specify a recipient) donates to Recipient 1. Someone who wanted to donate to Recipient 1, but for some reason immunologic reason could not, then donates a kidney to Recipient 2 (an unrelated person, but a good match). Someone related to Recipient 2 donates to an unknown person, and so on. The chain goes along until reaching a compatibility, age-related or other roadblock. Then a bridge NDD is used or a new chain is initiated with a new NDD or a deceased donor.
In 2012, members of the largest chain to that point—consisting of 60 donors and recipients—celebrated their success. To accomplish these matches, transplant specialists were sending and receiving donations across the country and finding that these transported kidney grafts were just as successful as single-site transfers.
With the progression of computer-aided matching capabilities and access to data via the National Kidney Registry, the number and length of donor chains has the potential to grow significantly, if not exponentially. The process enables a level of potential matching that literally is not possible without data analytics. By entering blood type, HLA antigens and antibodies, age, health condition and numerous other data points, the match potential of 500 incompatible pairs produces 30 billion possible combinations. Data of this magnitude can now be processed to come up with best matches.
The Kidney Registry has used their algorithm, Simultaneous Mutually Exclusive Loops and Chain Matching (SMELAC), to facilitate 309 transplantations from January to September 2017.
As elegant as the donor chain concept is, it suffers from two limitations that affect the number of donors and the length of a chain. First, it doesn’t address the chronological incompatibility between a donor and the relative he or she wishes to “insure” with a kidney for some future time when the need becomes urgent. Second, with a standard chain, the pool of people able to start or participate in a traditional donor chain is limited to those whose relatives need a kidney now.
Fortunately, UCLA’s kidney voucher program addresses these limitations. The details of this program will be discussed in the next blog post.